Various systems and methods for transportation of microscopic objects for various applications are presently in use.
U.S. Pat. No. 5,998,129 discloses the use of photokinetic impulse from pulsed laser beam to transport cells or a portion of tissue section that has been cut by the laser beam or by any other method. Due to the impulse the object to be transported is accelerated and transferred to a container placed behind the objects. However the use of photo-kinetic impulse from a pulsed laser beam to transport the microscopic objects can neither be used for intra-cellular transport nor transport in transverse plane (plane perpendicular to laser beam propagation).
U.S. Pat. No. 4,887,721 involves another method where the transportation of cells is attained by axial light scattering force and uses a weakly focused or collimated laser beam. In this method the scattering force dominates axial gradient force and the particle is propelled along the direction of the beam. (Other references which teach such similar method include Ashkin et. al, Phy.Rev.Lett., 24(4), 156-159(1970); Buican et. al., Applied Optics, 26 (24), 5311-5316 (1987); M. Uchida, M. Sato Maeda and H. Tashiro, Current Biology, 5(4), 380-382 (1995)). However, in this method of transportation, axial light scattering force can lead to transportation only in the direction of light generating the scattering force and transportation in directions other than this require use of additional beams and fabrication of special chambers and is therefore not generally applicable. Further such method cannot be used for intra-cellular transport and transport in transverse plane (plane perpendicular to laser beam propagation).
WO 0023825 discloses the use of laser light to trap particles within a hollow region of a hollow core optical fiber and transport the trapped particles along the fiber. Laser induced optical gradient forces trap the particles close to the center of the fiber and axial scattering force propels along the length of the hollow fiber. Such method of laser guided transport of particles inside hollow optical fiber cannot be used for intra-cellular transport and is also limited by maneuverability of the guiding optical fiber.
U.S. Pat. No. 5,212,382 discloses yet another method of transporting optically trapped objects by scanning the trapping beam or the microscope stage. (Similar method is also disclosed by Block, S. M., Non-invasive technique in cell biology. J. K. Foskett and S. Grinstein, ed., New York, John Wiley and sons 375-402(1990); Kuo, S. C., and Sheetz, M. P., Trends Cell Biol. 2, 116-119 (1992); Weber, G., and Greulich, K. O., Int. Rev. Cytol. 133, 1-41 (1992)). While this method is most obvious method of optical transport the same has also certain limitations in terms of speed and the number of particle that can be transported simultaneously.
U.S. Pat. No. 5,363,190 discloses a method and system for optical trapping of object in a laser beam having a non-rotational symmetrical spatial property distribution and transport of the trapped object from one position on the specimen stage to the other by either moving the trap beam itself or by moving the specimen stage. Here the use of a non-rotational symmetrical elliptical trap beam helps orient an asymmetric object along the major axis of the trap beam and thus the object can be rotated in a plane transverse to the propagation direction of the trap beam by rotation of the laser trap beam. However, the method and system disclosed herein can only be used for transportation of a trapped object in the said manner and therefore suffers with the same limitations as for U.S. Pat. No. 5,212,382. Further, it cannot be used for channeling, accelerating and sorting of microscopic objects.